Well, the hardware store was a big help. They didn’t have a right-size router bit, and their wood selection was lacking. (And the ‘kid’ ‘helping’ me was pretty much slacking.) Here are the dimensions:
Mortises: 7/16 x 2⅜.
Face boards: 2⅜ x 11/16 x 60
Crosspieces/Leg ends: ⅞ x 2⅜ x 17½.
Slats: ¾ x 1½ x 60
They had some hemlock that was just about the right width for the face boards. I think they were like 2½ instead of 2⅜. I could live with that, as long as the tops are even with the slats. The wood for the crosspieces and the leg ends was 7/16 thick, and a little wider than original. I could deal with that, too. The wood for the slats? Yes, they had ¾-inch thick pieces; but they were about ⅜ inch too wide. Coincidentally, the spacing between the slats on the original table is ⅜ inch. So if I used those, my slat table wouldn’t have any spaces between the slats – unless I increased the width. Could do, but I’d like to try to keep the dimensions as close as possible to the original. (Besides, it’s been a long day. Ten slats plus 11 x ⅜ inch spacing = ?-inch crosspieces. I don’t know the width of the wood at the hardware store. 1 inch? 1⅛? Then, how long are the crosspieces? No energy to do the math right now.)
In other words, it was a bust. If I don’t go down to Olympia tomorrow, I’ll try Home Despot. I asked the lumber kid at the hardware store if there are any lumber yards around, and he could only suggest Home Depo or Lowe’s, so…
Incidentally, I mentioned the ‘leg ends’. I’d assumed the legs were put on the original with hanger bolts and discs. Turns out they’re screwed into a piece of wood that screws onto the crosspieces. Much simpler – and cheaper – solution than hanger bolts and mounting discs.